Method of producing precious metal alloy objects

ABSTRACT

The present invention provides a method for manufacturing a biocompatible precious metal alloy object. According to a first aspect melting of alloying elements and casting of the biocompatible precious metal alloy are carried out in a process chamber ( 11 ) being provided with a process gas of predetermined composition. A burning flame ( 19 ) of a hydrocarbon-containing gas provides low oxygen and water content. According to a second aspect post-processing of a precious metal alloy is made in atmosphere provided by the process gas to form the biocompatible precious metal alloy object. The biocompatible precious metal alloy object manufactured according to the invention has a low probability of causing sensitisation when in contact with the human body.

TECHNICAL FIELD OF THE INVENTION

The present invention relates to precious metal alloys and methods ofmanufacturing such. In particular the present invention relates toprecious metal alloy objects such as jewellery and other precious metalcontaining objects, for example dental implants and decorative members,that are intended to be in contact with a human body.

BACKGROUND OF THE INVENTION

Precious metals are commonly used in jewellery or other objects whichare intended to be in contact with the human body. One reason for thisis that precious metals are less reactive than most elements. Another istheir high economical value. Moreover, precious metals usually have anattractive lustre and high ductility. The most well-known preciousmetals are gold and silver, but other precious metals such as platinumand palladium are commonly used for the same purposes.

Precious metal objects which are worn on the human body are subjected towear and damage. The ductility of precious metals is an advantage sincethe risk for fracture is low, but precious metals have relatively lowhardness making them susceptible to wear. To make them harder, and alsodue to the high cost of the precious metals, precious metals used injewellery, implants, etc. are usually alloyed with other elements. Theprecious metals may also be alloyed to improve other properties of theprecious metal, such as for example to obtain a certain lustre or colouror to improve the workability.

It is known that some people cannot wear jewellery or other decorativemembers due to hypersensitivity or allergy, which may cause dermatitisor allergic reactions. The allergenic potency of different elementsdiffers and generally precious metals have the lowest potency. Among thealloying elements commonly used for gold, nickel has been identified ashaving the highest allergenic potency. Therefore the nickel release in asynthetic sweat solution has been established as a measure on theallergenicity of a nickel-containing material, and a threshold level(0.2 μg/cm²/week) below which an object may be considered non-allergichas been defined in the European Union “Nickel Directive” (94/27/EC).Similar threshold levels for other alloying elements have not beenestablished, but it is likely that other alloying elements, even silver,copper and gold, may also cause sensitisation. Allergenic reactions orthe like may also occur due to impurities in the precious metals ormetal alloys. The impurities may appear due to impurities of the rawmaterials used or due to the manufacturing of the alloy. For exampleimpurities may be added if the precious metal or metal alloy is treatedwith an acid in a step following a casting step to remove oxides formedon the cast object. Irrespective of the reason for the sensitisation, aprecious metal object can be regarded as biocompatible if theprobability of causing sensitisation is below a certain degree.

One common belief is that allergenic reactions do not occur if only purealloying elements of precious metals are used. Using conventionalmanufacturing methods this does not necessarily yield a precious metalalloy that is non-allergenic and more important the semi-finished orfinished product may not have e.g. the required hardness, fracturetoughness, workability, colour, etc. As mentioned above the hardness ofa precious metal or metal alloy is important to provide wear resistance.By way of example, a gold alloy comprising the alloying elements gold,silver and copper is usually manufactured by melting the alloyingelements in a crucible and casting them in a mould to form a rawmaterial that subsequently is subjected to further processing to formthe final object. In manufacturing of a precious metal alloy object, theraw material is typically cold or hot worked and it may be subjected toheat treatments and/or cooling steps necessary to obtain certainmaterial properties in the final object. This process is by no meanssimple, e.g. an increased hardness due to e.g. strain hardening duringcold working of the raw material may cause difficulties due to decreasedworkability and on the contrary hot working of the raw material maysignificantly decrease the workability of the alloy making it difficultto form the final object. Also the alloy may be brittle after thecasting of the raw material, making additional annealing stepsnecessary.

SUMMARY OF THE INVENTION

The prior art has drawbacks with regard to being able to provide aprecious metal alloy object that is biocompatible and has the desiredmaterial properties, such as high hardness and good workability.

The object of the present invention is to overcome the drawbacks of theprior art. This is achieved by a biocompatible precious metal alloyobject and a method for manufacturing such as defined in the independentclaims.

The method for manufacturing a biocompatible precious metal alloy objectaccording to the present invention comprises the step of forming thebiocompatible precious metal alloy object in a process chamber. Themethod further comprises the step of providing a process gas ofpredetermined composition having a water content of less than 0.005 kgH₂O per kg process gas and an oxygen content of less than 5%. Theprocess gas is provided in the process chamber at least during saidforming of the biocompatible precious metal alloy object.

According to a first aspect of the present invention the step of formingthe biocompatible precious metal alloy object comprises the steps ofmelting alloying elements together in order to form the precious metalalloy, and casting the molten alloying elements of the precious metalalloy.

According to a second aspect of the present invention the step offorming the biocompatible precious metal alloy object comprises the stepof post-processing a precious metal alloy, i.e. a raw material, in theprocess chamber to form the biocompatible precious metal alloy object.Preferably the raw material is manufactured in accordance with themethod of the present invention. The post-processing may for exampleinclude soldering and/or welding.

According to one embodiment of the present invention a solder alloy,suitable for being used in the above mentioned soldering of the preciousmetal alloy raw material or object, is manufactured in accordance withthe method of manufacturing the biocompatible precious metal alloyobject according to the first aspect.

In one embodiment of the present invention the content of the processgas and hence the environment in the process chamber is controlled byburning a flame that is supplied with a hydrocarbon-containing gas.Thereby oxygen present in the process chamber is combusted.

The bulk of a biocompatible precious metal alloy object that has beenmanufactured according to the method of the present invention has anoxygen content of less than 5 μg/g, preferably less than 3 μg/g and morepreferably less than 1 μg/g; and a hydrogen content of less than 0.05μg/g, preferably less than 0.01 μg/g and more preferably less than 0.005μg/g.

A biocompatible precious metal alloy object according to the presentinvention preferably comprises 2% Ag. More preferably it is a gold alloyof more than 14 carat or a silver alloy.

Thanks to the invention it is possible to provide a biocompatibleprecious metal alloy object which is not likely to cause sensitisationwhen in contact with a human body.

It is a further advantage of the invention to provide a precious metalalloy object which has tailored material properties with regards to e.g.hardness and workability. Such an object can be used as a raw materialthat is subjected to post-processing in order to form a final preciousmetal alloy object having adequate material properties such as highhardness and high fracture toughness.

It is a yet further advantage of the invention to providepost-processing of a biocompatible precious metal alloy raw materials ina dedicated workstation to substantially maintain the tailored materialproperties of the biocompatible precious metal alloy raw material whichpreferably has been manufactured according to a method in accordancewith the present invention.

Embodiments of the invention are defined in the dependent claims. Otherobjects, advantages and novel features of the invention will becomeapparent from the following detailed description of the invention whenconsidered in conjunction with the accompanying drawings and claims.

BRIEF DESCRIPTION OF THE DRAWINGS

Preferred embodiments of the invention will now be described withreference to the accompanying drawings, wherein:

FIGS. 1 a-d are schematic diagrams of embodiments of a method ofmanufacturing a precious metal alloy object according to the presentinvention;

FIGS. 2 a-b are schematic illustrations of process chambers according tothe present invention;

FIG. 3 is a schematic illustration of a crucible arranged on a mouldwith an intermediate pre-heater chamber according to the presentinvention;

FIG. 4 is a schematic diagram of a method in accordance with the presentinvention for manufacturing a precious metal alloy comprising the stepof evacuating the mould; and

FIG. 5 is a schematic illustration of a process chamber suitable forpost-processing according to the invention.

DETAILED DESCRIPTION OF EMBODIMENTS

During manufacturing of a precious metal alloy object the alloyingelements are usually melted and subsequently cast to form a preciousmetal alloy object, a so-called raw material, which subsequently issubjected to post-processing, including e.g. forging, welding,soldering, casting, grinding, polishing or drawing, to form a preciousmetal alloy object such as a jewellery. One object of the presentinvention is to provide a method for manufacturing of precious metalobjects which are biocompatible so that they do not cause sensitisationwhen carried in contact with the human body. Examples of such objectsare jewellery (including piercing jewellery), decorative members ofother kind, dental implants, etc. as well as the raw material mentionedabove. The precious metal alloy composition according to the presentinvention comprise of precious metal alloys compositions commonly usedfor e.g. jewellery, dental implants, and decorative members. Examples ofsuch, however not limited to these, are gold (22K, 18K, 14K, etc.) andsterling silver. Although a gold alloy manufactured according to thepresent invention may be of a certain carat it may differ slightly inthe content of the main alloying elements (Au, Ag, Cu) and theadditional alloying elements may differ in content or composition toobtain e.g. a certain lustre. Furthermore, although the term alloy isused, the present invention is not limited to alloys comprising two ormore materials. Also pure precious metals may be manufactured using themethod of the present invention.

Referring to FIGS. 1 a-d, a method for manufacturing a biocompatibleprecious metal alloy object that is made of a precious metal alloyaccording to the present invention comprises the steps of:

-   -   100 forming the biocompatible precious metal alloy object in a        process chamber; and    -   at least during said forming 101 providing a process gas of        predetermined composition in the process chamber 11, wherein the        process gas has a water content of less than 0.005 kg H₂O per kg        of process gas and an oxygen content less than 5% oxygen.

In one embodiment of the present invention the step of forming furthercomprises the steps of:

-   -   102 melting alloying elements together in order to form the        precious metal alloy; and    -   103 casting the molten alloying elements of the precious metal        alloy, wherein the steps of melting and casting are carried out        within the process chamber 11 in a controlled atmosphere        comprising the process gas.

In another embodiment of the present invention step of forming comprisesthe step of 111 post-processing the precious metal alloy in the processchamber 11 to form the biocompatible precious metal alloy object. Thepost-processing is preferably performed on a precious metal alloy rawmaterial that has been manufactured according to the above mentionedsteps of melting and casting. However, the invention is not limited tothis and suitable raw materials manufactured according to other methodscan be used. The post-processing may be made in the same process chamber11 as used in the manufacturing of the raw material or in anotherprocess chamber such as a dedicated workstation chamber.

In one embodiment of the present invention the step of providing theprocess gas further comprises the step of 104 combusting oxygen of theprocess chamber 11 using a flame 19 that is supplied with ahydrocarbon-containing gas.

Referring to FIGS. 2 a-b, the process chamber 11 is preferably designedsuch that a controlled atmosphere that is separated from the ambient aircan be provided in the process chamber 11. In one embodiment of thepresent invention the step of providing the process gas comprises thestep of generating an overpressure in the process chamber 11 in order tohave a net flow of gas from within the process chamber 11 to theoutside, for example by using a check valve or a pump. A suitableoverpressure can also be maintained by having a net flow through doorsof an airlock system 28. This also automatically provides a controlledatmosphere in the airlock system.

FIG. 2 a schematically illustrates a process chamber 11 according to oneembodiment of the present invention. A process gas of predeterminedcomposition is provided in the process chamber 11, preferably before andduring melting and casting of alloying elements, by combusting burning aflame 19 that is supplied with a hydrocarbon-containing gas within theprocess chamber. The combustion process lowers the oxygen content of theprocess chamber 11 to at least less than 5%, preferably less than 2% andmore preferably to less than 1%. In addition dehydration means 21 may beused. This limits the water content of the process gas to at least lessthan 0.01 kg H₂O per kg air, preferably less than 0.005 kg H₂O per kgair, and most preferably less than 0.001 kg H₂O per kg air. The processchamber 11 may further comprises a crucible 13 arranged on a mould 15,which, for example, may be a so-called flask comprising a plastercompound inside, which a skilled person is familiar with. The alloyingelements are provided in the crucible 13 and melted. The mould 15 is atleast partly filled by the molten alloying elements and aftersolidification of the molten alloying elements a precious metal alloyobject is formed in the mould 15.

FIG. 2 b schematically illustrates a process chamber 11 suitable for themelting and casting according to one embodiment of the presentinvention. A process gas of predetermined composition in the processchamber 11 is accomplished by supplying a hydrocarbon-containing gas toa burning flame 19 within the process chamber 11. By way of example thehydrocarbon-containing gas may be a mixture of oxygen and acetylene,i.e. a welding flame, wherein the oxygen/acetylene ratio is adjusted togive a reducing flame (an over-rich mixture). The combustion processlowers the oxygen content of the process chamber 11 to at least lessthan 5%, preferably less than 2% and more preferably to less than 1%. Inaddition dehydration means 21 are used to limit the water content of theprocess gas to at least less than 0.01 kg H₂O per kg air, preferablyless than 0.005 kg H₂O per kg air, and most preferably less than 0.001kg H₂O per kg air. The process chamber 11 may further comprise acrucible 13 arranged on a mould 15, which may be a so-called flaskcomprising a plaster compound. The alloying elements are provided in thecrucible 13. Inductive heating by inductive heaters 25 may be used tomelt the alloying elements, which subsequently are supplied as a melt tothe mould 15, for example through an openable and closable opening inthe bottom of the crucible 13. After solidification of the melt aprecious metal alloy object is formed in the mould 15.

In one embodiment of the present invention the step of providing saidfirst process gas further comprises the step of supplying a protectivegas such as nitrogen, argon, etc. to the process chamber 11. Thisprotective gas can be used as means for removing ambient air from theprocess chamber and also can function as an inert gas during melting andcasting.

In one embodiment of the present invention the step of providing saidfirst process gas comprises the step of 106 drying the first process gasof predetermined composition using dehydration means 21. This can beachieved, for example, by water vapour in the first process gas beingcondensed onto a cold surface and led to a drain.

In one embodiment of the present invention the method further comprisesthe step of evacuating a gas from the mould 15 prior to the casting ofthe molten alloying elements e.g. by connecting a vacuum pump to one endof the mould 15.

In one embodiment of the method according to the present invention thestep of evacuating further comprises drying of an inert gas, optionallypre-heating of the inert gas, and providing a flow of the optionallypre-heated inert gas through the mould before casting. The inert gas maybe provided from the process gas of pre-determined composition. Onealternative is to supply an inert gas of another composition. Inert gasis for the purpose of this application interpreted to mean a gas havinga water content of less than 0.005 kg H₂O per kg air and an oxygencontent of less than 5% oxygen.

In one embodiment of the invention the drying of the inert gas isobtained using dehydration means 21 in the form of e.g. a refrigerationdrier. Gas from the process chamber 11 is pumped into the refrigerationdrier, wherein water vapour in the gas is condensed and removed from thegas. The dried gas may then be fed back to the process chamber 11.

Referring to FIG. 3, in one implementation of the method of the presentinvention the mould 15 is preheated, e.g. in a separate oven, to about350-400° C. Thereafter, a pre-heater chamber 17, a mould 15 and acrucible 13 are assembled with the mould 15 underneath the crucible 13.Alloying elements are provided in the crucible 13. Heater means, forexample, inductive heaters 25, are used to heat the crucible 13 to atemperature which is sufficient to melt the alloying elements. Thetemperature depends on the composition of the alloying elements but maybe about 900° C. The pre-heater chamber may be heated by heattransferred from the crucible 13. The temperature of the pre-heaterchamber 17 may be about 600° C. A pressure gradient is applied over themould 15, e.g. by applying a vacuum pump to one end, i.e. an outlet, ofthe mould 15, in such way that the process gas of the process chamber 11is sucked into the pre-heater chamber 17 and gets preheated beforeentering the mould 15. This gives a preheating of the mould 15 which isat least sufficient for maintaining the temperature obtained after thepreheating. By supplying the mould through an inlet of the mould with agas having a controlled composition to provide a flow of the gas throughthe mould the conditions for casting a biocompatible object is improved.Residual oxygen and water trapped in the mould may be forced out of it.By way of example the crucible may have an exit hole in the bottom,which initially is sealed using a rod. When the alloying elements havemelted and reached the desired temperature the rod can be removed andthe melt is poured down into the preheated mould 15. The method of thepresent invention results in precious metal objects having substantiallyno oxidation layer. One advantage with this is that no subsequenttreatment in an acid bath (as is commonly used in the prior art) isrequired. Treatment in such acid baths is believed to be one source ofimpurities which may give sensitisation for a carrier of a preciousmetal alloy object manufactured from the acid bath-treated rawmaterials.

Referring to FIG. 4, in one embodiment of the present invention whereinalloying elements are melted in a crucible 13 and a biocompatibleprecious metal alloy object is casted in a mould 15 within a processchamber 11 having an atmosphere of a process gas of predeterminedcomposition, the method comprises the steps of:

-   -   optionally 107 pre-heating the mould 15 before casting in said        mould 15,    -   108 pre-heating an inert gas in a pre-heater chamber 17 arranged        in-between the mould 15 and the crucible 13, and    -   109 flowing the inert gas through the mould 15 by evacuating the        inert gas from the one end of the mould 15.

A pre-heater chamber according to the invention may comprise acylindrical body having holes around the perimeter to allow gas from theatmosphere of the process chamber to enter into a through bore which isopen for the melted alloying elements to be supplied to the mould. Hencethe gas enters the pre-heater chamber from the side and is sucked downinto the mould.

As mentioned above, the step of casting comprises solidification of themelted alloying elements in the mould 15. In one embodiment of themethod of the present invention the cooling of the solidified preciousmetal alloy object resulting from the solidification of the moltenalloying elements is made in a controlled environment such as anatmosphere of the process gas of predetermined composition in theprocess chamber. The cooling may be performed e.g. within the processchamber or in an adjacent chamber which can be entered from the processchamber without exposing the mould to the ambient air.

In one embodiment of the method of the present invention the mould withthe solidified precious metal alloy object is quenched in analcohol-containing water bath having a temperature of less than 5° C.

The bulk of the precious metal alloy object that has been manufacturedaccording to a method in accordance with the present invention will havean oxygen content of less than 5 μg/g, preferably less than 3 μg/g andmore preferably less than 1 μg/g. In addition, the bulk of the preciousmetal alloy object that has been manufactured according to the method ofthe present invention will have a hydrogen content of less than 0.05μg/g, preferably less than 0.01 μg/g and more preferably less than 0.005μg/g. The surface layer of the same precious metal alloy object willhave an oxygen content of less than 30 μg/g, preferably less than 20μg/g and more preferably less than 10 μg/g and a hydrogen content ofless than 3 μg/g, preferably less than 2 μg/g and more preferably lessthan 1 μg/g. The oxygen and hydrogen content of the precious metal alloyobject are important for their mechanical properties, in particular ifthe cast precious metal alloy object is a raw material that is going tobe worked by a goldsmith to form for example jewellery. High hydrogencontent may, for example, give a hard and brittle alloy which is noteasily post-processed by a goldsmith. This phenomenon is known in thefield of metallurgy as hydrogen embrittlement. A method for testing thehydrogen and oxygen content in the surface layer comprises heating ofthe precious metal alloy object to a temperature close to, but below,the melting temperature of the alloy and then measuring the residualgases. At this temperature only gases originally trapped in the surfaceof the alloy object are released. The bulk values have been obtained ina similar way but by heating the alloy object to a temperature wellabove the melting temperature so that gases originally trapped in thebulk of the alloy object are released.

In one embodiment of the present invention the precious metal alloyobject comprises at least 2% Ag. Examples of such precious metal alloysare 18 carat gold, 14 carat gold, Sterling silver etc.

Referring to FIG. 5, the advantageous properties of the precious metalalloy object of the present invention may be ruined by impropertreatment of e.g. a goldsmith in his post-processing to form e.g.jewellery of the precious metal alloy object, i.e. a raw material, whichhas been manufactured in accordance with the method of the presentinvention. Hence, in one embodiment of the present invention a processchamber that is a dedicated workstation chamber for post-processing of aprecious metal alloy in accordance with the method of the presentinvention is provided. The precious metal alloy is preferablymanufactured according to the method of the present invention, but thisembodiment is not limited to this. In one embodiment of the presentinvention the workstation chamber is a glove box, i.e. a closed chamberhaving two gloves extending into the chamber.

Any kind of machining that normally is performed on precious metalalloys objects can benefit from being performed within the workstationchamber. In particular, if biocompatible precious metal alloy has beenformed e.g. using the method of the present invention, the properties ofthat alloy can be maintained using this workstation. Using conventionaltechniques there is an overwhelming risk that the advantageousproperties are ruined. Examples of machining that can be performed arecold working, hot working, soldering, drawing, forging, polishing, etc.

In one embodiment of the invention the method further comprises the stepof soldering and/or welding of a precious metal alloy object, whichpreferably has been melted and cast according to the method of thepresent invention, in the process gas of the process chamber or thededicated workstation chamber. A typical solder for soldering preciousmetal alloy objects of the present invention is a precious metal alloyitself. Preferably the solder is fabricated in the same way as theprecious metal alloy object of the present invention in a processchamber having a process gas of predetermined composition, i.e. having awater content of less than 0.005 kg H₂O per kg process gas and an oxygencontent of less than 5%.

The method for manufacturing a biocompatible precious metal alloy objectcan be used to manufacture a solder alloy as well. A method formanufacturing a solder according to the present invention comprises thesteps of providing a process gas of predetermined composition in aprocess chamber, the process gas having a water content of less than0.005 kg H₂O per kg air and an oxygen content less than 5% oxygen;melting solder elements; and casting the molten solder elements to formthe solder, by way of example in the form of a rod or a block, whereinthe steps of melting and casting are carried out within the processchamber. Preferably the step of providing further comprises the step ofcombusting oxygen of the process chamber using a flame that is suppliedwith a hydrocarbon-containing gas. By way of example thehydrocarbon-containing gas may be a mixture of oxygen and acetylene,i.e. a welding flame, wherein the oxygen/acetylene ratio is adjusted togive a reducing flame. The combustion process lowers the oxygen contentof the process chamber. Dehydration means may be used to limit the watercontent of the process gas. In one implementation of the method formanufacturing of a solder alloy the process chamber comprises a cruciblearranged on a mould. The solder elements are provided in the crucible.Heating, for example by inductive heaters may be used to melt thealloying elements, which subsequently are supplied to the mould, by wayof example through an opening in the bottom of the crucible. Aftersolidification of the melt a solder alloy is formed in the mould.Optionally the step of providing further comprises the step of supplyinga protective gas such as nitrogen, argon, etc. to the process chamber.This protective gas can be used as means for removing ambient air fromthe process chamber and also work as an inert gas during melting andcasting.

While the invention has been described in connection with what ispresently considered to be the most practical and preferred embodiments,it is to be understood that the invention is not to be limited to thedisclosed embodiments, on the contrary, it is intended to cover variousmodifications and equivalent arrangements within the appended claims.

1-17. (canceled)
 18. A method for manufacturing a biocompatible preciousmetal alloy object made of a precious metal alloy, wherein the methodcomprises the step of (100) forming the biocompatible precious metalalloy object in a process chamber (11), and the step of at least duringsaid forming (101) providing a process gas of predetermined compositionin the process chamber (11), characterised in that the process gas has awater content of less than 0.005 kg H₂O per kg of process gas and anoxygen content of less than 5%.
 19. The method according to claim 18,wherein the step of forming comprises the steps of (102) meltingalloying elements together in order to form the precious metal alloy,and (103) casting the molten alloying elements of the precious metalalloy.
 20. The method according to claim 18, wherein the step of formingcomprises the step of (111) post-processing the precious metal alloy inthe process chamber (11) to form the biocompatible precious metal alloyobject.
 21. The method according to claim 18, wherein the step ofproviding the process gas comprises the step of (104) combusting oxygenpresent in the process chamber (11) using a flame (19) that is suppliedwith a hydrocarbon-containing gas.
 22. The method according to claim 18,wherein the step of providing the process gas comprises the step ofdrying the process gas using dehydration means (21).
 23. The methodaccording to claim 19, further comprising the step of evacuating a gasfrom a mould (15), and wherein the step of casting comprises the step ofat least partly filling the mould (15) with the molten alloyingelements.
 24. The method according to claim 23, further comprising thestep of flowing an inert gas (8) through the mould (15).
 25. The methodaccording to claim 24, wherein the inert gas (8) comprises process gasextracted from the process chamber (11).
 26. The method according toclaim 24, further comprising the step of pre-heating the inert gas (8)in a pre-heater chamber (17) arranged in between a crucible (13) formelting the alloying elements and the mould (15).
 27. The methodaccording to claim 18, wherein the step of casting comprises the step ofcooling the moulded precious metal alloy in the process gas withoutexposing it to ambient air.
 28. The method according to claim 19,wherein the step of post-processing comprises soldering and/or weldingof the precious metal alloy.
 29. The method according to claim 28,wherein the soldering is performed using a solder alloy that ismanufactured a solder alloy in the process gas of the process chamber.30. A biocompatible precious metal alloy object, characterised in thatthe biocompatible precious metal alloy object is manufactured accordingto the method of claim 18 and the bulk of the biocompatible preciousmetal alloy object has an oxygen content of less than 5 μg/g, preferablyless than 3 μg/g and more preferably less than 1 μg/g; and a hydrogencontent of less than 0.05 μg/g, preferably less than 0.01 μg/g and morepreferably less than 0.005 μg/g.
 31. The biocompatible precious metalalloy object according to claim 30, wherein the biocompatible preciousmetal alloy object comprises at least 2% Ag.
 32. The biocompatibleprecious metal alloy object according to claim 30, wherein thebiocompatible precious metal alloy object is a gold alloy of more than14 carat.
 33. The biocompatible precious metal alloy object according toclaim 30, wherein the biocompatible precious metal alloy is a silveralloy.
 34. The biocompatible precious metal alloy object according toclaim 30, wherein the surface layer of the biocompatible precious metalalloy object has an oxygen content of less than 30 μg/g, preferably lessthan 20 μg/g and more preferably less than 10 μg/g; and a hydrogencontent of less than 3 μg/g, preferably less than 2 μg/g and morepreferably less than 1 μg/g.
 35. The method according to claim 18,wherein the step of forming comprises the step of (111) post-processingthe precious metal alloy in the process chamber (11) to form thebiocompatible precious metal alloy object.
 36. The method according toclaim 25, further comprising the step of pre-heating the inert gas (8)in a pre-heater chamber (17) arranged in between a crucible (13) formelting the alloying elements and the mould (15).